Recent interest in the development of new energy sources has resulted in the recognition of solar power as an important replacement for the diminishing sources of conventional energy. Rapid development of solar technology has been fostered by space exploration programs, and solar energy cells of various types are now commercailly available. Unfortunately, the cost of commercial solar energy cells often makes them impractical for use in small, low cost appliances.
For a number of years there has been experimentation in the use of solar energy to power small, portable electrical appliances. Portable radios are an example of an appliance which is uniquely suited for use with a solar power source, for such radios are generally operated from a self contained power supply when used on beaches and in other outdoor environments. Similarly, small outdoor toys such as model boats, autos, trucks, helicopters, tractors and airplanes might well be powered by solar energy as well as other movable outdoor devices such as yard ornaments, fountains, etc.
Previous attempts to develop an economical solar power source capable of operating effectively with low cost portable appliances such as radios have not been commercially successful. Small, solid state radios are capable of operating from a 11/2 volt power supply with a current requirement range of from 12 to 50 milliamps. A conventional battery has the capability to supply a stable 11/2 volt requirement as well as a wide current range (0 to 300 + milliamps). However, a conventional solar cell power supply will provide no such stability because of the variable degree of light which the sun supplies. With even small, solid state portable radios, normal variations in sun angle and intensity will radically change the current and voltage operating constants provided by a solar cell power source, and thus will result in periods of insufficient voltage and/or current to maintain satisfactory radio reception. conversely, a brilliant sun may overpower the radio circuit thereby creating audio distortion. The wide range of voltage and current fluctuations from the solar power source cause variations in audio oscillation and audio distortion which, as a practical matter, render commercially useless a radio powered directly from a conventinal solar power source.
Proposals have been made to power radios directly from solar power cells as illustrated by U.S. Pat. No. 3,205,482 to Taylor et al. Possibly this would be feasible but not reliable for emergency radio use where no other power source is available and erratic periods of distorted audio reception are better than no reception at all. Otherwise, such a direct solar powered radio receiver would be completely unsuitable for conventional use.
To offset to some extent the voltage and current fluctuations in a solar power source output resulting from solar light variations, it would be possible to overpower a use device, such as a radio, and thereby achieve some stability. A commerically available silicon solar cell with 10% efficiency provides a 0.4 volt output per cell, while the current output of each cell is a direct function of cell size. Thus a large power source having a large number of solar cells to provide a high voltage output and a large effective area to provide a high current output could be employed to power a small radio. If excess voltage and current were provided which equal in magnitude the projected current and voltage drops resulting from sun intensity variations plus the peak demands of the radio audio excursions, then direct solar cell power could possibly be employed to achieve acceptable radio operation. This solution is prohibitively expensive, for the cost of solar cells is high; i.e., $100 per watt for silicon cells.
To minimize the number of solar cells required to effectively power a radio, such cells have been used in combination with a battery. The cells operate through a charging circuit to charge the battery which then powers the radio. U.S. Pat. No. 2,919,353 is typical of the prior art relating to this type of battery charging system.
Ideally, a solar power source for small electrical devices should have the ability to furnish a substantially stable power output directly to an electrical device without requiring the use of an intermediate battery and battery charging circuit. To achieve economy, the minimum number of solar cells necessary to provide the normal operating voltage for the electrical device should be used, and the size of the cells should be limited to the minimum size necessary to provide a normal operative current range.
It is a primary object of the present invention to provide a novel and improved solar power source capable of providing substantially stable electrical energy directly to an electrical unit. Sun-power is translated to useable power through conversion of sunlight into electrical energy by means of silicon crystal solar cells or other known solar cells. No batteries of any kind are required, although a battery may be used as a completely separate, independent source of power.
Another object of the present invention is to provide a novel and improved solar power source for use as a direct, primary electrical power source for an electrical unit which places a varying current demand on the power source. The solar power source includes a plurality of solar cells designed to provide the normal voltage and current requirements of the electrical unit supplied therefrom and a large capacitor across the output of the solar cells provides a current reserve to satisfy the peak demands of the electrical unit and offset the effects of variations in sunlight.
A further object of the present invention is to provide a novel and improved solar power source for use with portable electrical units which includes a solar cell thermal shielding assembly to facilitate uniform solar cell operation during long periods of exposure to direct sunlight.
A still further object of the present invention is to provide a novel and improved solar powered radio receiver which includes a direct solar power source consisting of solar cells designed to provide the normal operating current and voltage requirements for the radio receiver. The solar cells are mounted on the top surface of the receiver beneath a thermal shield, and a large capacitor is connected across the cell output to provide a current reserve to satisfy peak current demands and to offset the effects of variations in sunlight.